The four suffered minor cuts during the confrontation around 11:15 p.m. Tuesday at the Clark and Division stop, police said, citing preliminary information.

The Guardian Angels were on the platform, waiting to get on a train, when they spotted a man hitting a passenger and taking his iPhone 4S, police said. They intervened and a second man pulled a knife and cut three of the Guardian Angels on their arms and the fourth on the head, authorities said.

The robbers ran off and grabbed a cab, police said.

Wednesday evening, police released CTA surveillance photos of the suspects and asked for the public's help in finding them.

Miguel Fuentes, the head of the local Guardian Angels chapter, said he had spotted one of the robbers standing suspiciously close behind the passenger on the northbound train.

"As the train's pulling up, I noticed (the robber) hovering around (the victim) from behind. So the passenger had no clue," Fuentes said hours after the attack left him with 17 stitches in his right arm.

As the train pulled to the stop, Fuentes said he saw the robber pull a handgun and hit the passenger from behind. "People get up, they start running. . .They're screaming. The train still hadn't made a complete stop," Fuentes said.

Fuentes said he grabbed the robber's arm as he was fleeing the train and tucking the pistol into his waistband. The robber managed pulled away and ran toward the turnstile, where the three other Guardian Angels were waiting.

Fuentes and the three other volunteers subdued the robber but a second man who had also been on the train approached them from behind.

"He said, 'What's going on? Let him go!' " Fuentes said.

The second man then pulled out a folding knife and hit the Guardian Angels, then flipped out the blade and began stabbing Fuentes and the others.

"We had no choice but to let the guy go because we were all bleeding," Fuentes said.

The attackers ran from the train platform and got a cab, police said. They ditched it without paying near Oak and Orleans streets. Detectives were canvassing the area around the train station and checking surveillance cameras, police said.

Fuentes said he and the others, all in their 20s, were treated for minor wounds. The robbery victim was also treated.

Known by their red berets, the Guardian Angels often patrol CTA stations and neighborhood streets. The group has 130 chapters in 17 countries, according to the group's website.

Fuentes, a 25-year veteran of the Guardian Angels, said he had no regrets about intervening. "If we don't do something, someone could get hurt or killed," he said.

Anyone with information or photographs can call Area Central detectives at 312-747-8384.

Guardian Angels members (from left) Erik Eulogio, Michael Fuentes, Thomas Hunt and Mario Rodriguez outside the CTA Red Line Clark and Division Stop early Wednesday, after having stab wounds treated at the hospital. They were stabbed while holding down a man who pistol-whipped a CTA rider.

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